In typical systems utilizing steam to supply energy for heating, cooking or mechanical work, the steam has a tendency to condense into water as it expends its energy. This water or condensate must be removed from the steam piping system to prevent it from interfering with the piping system or the mechanisms utilizing the steam energy. Thus, steam piping systems must be provided with equipment for removing the condensate.
Mechanical devices, such as steam traps, were and still are widely used to remove or drain condensate from steam piping systems. These devices are designed to prevent the escape of live steam by attempting to distinguish steam from condensate, usually by differentiating temperature, buoyancy effects or thermodynamic properties. Steam traps are basically valves that employ moving parts and operate intermittently, remaining closed until a predetermined amount of condensate has collected, then opening to allow the condensate to pass through, typically to a boiler return line. Because these steam traps employ moving parts and are usually subject to harsh operating conditions, they have a tendency to fail, often in the open position. Steam trap failures result in substantial steam losses, which require the production of additional steam at the expense of increased fuel consumption.
Continuous flow orifice or venturi nozzle condensate removal devices were designed to overcome the problems associated with intermittently operating mechanical steam traps. The continuous flow condensate removal devices operate on the principle of two-phase fluid flow and do not employ moving parts. In these continuous flow devices, the mixture of steam and condensate flowing through the steam piping system is directed toward an orifice or venturi nozzle. When properly sized, a constricted passageway within the orifice or venturi nozzle causes the condensate, which is much denser and moves at a much slower speed than that of the steam, to interfere with the flow of steam. The area immediately upstream of the constricted passageway becomes, essentially, obstructed by the condensate, which therefore blocks the flow of steam, while the resulting pressure from the steam forces the condensate through the orifice or nozzle.
Several such continuous flow condensate removal devices are disclosed in U.S. Pat. Nos. 4,486,208 and 4,426,213 to Stavropoulos, and U.S. Pat. No. 4,745,943 to Mortensen. Stavropoulos discloses devices having a generally cylindrical body which houses a coaxially aligned, generally cylindrical bore between a converging conical entrance formation and a diverging conical exit formation. An elongated tubular nozzle structure is removeably mounted within the bore and is provided with an internal constricted passageway therethrough, which is sized according to certain predetermined characteristics of a particular steam flow application to sufficiently block the flow of steam while allowing for the discharge of condensate. The tubular nozzle structure is replaceable with other tubular nozzle structures having different size constricted passageways to meet varying steam flow applications.
Mortensen discloses a similar steam condensate removal device, wherein the venturi-type nozzle structure is formed integrally within the generally cylindrical body between an upstream condensate collection passageway and a downstream conical discharge passageway. The constricted passageway within the nozzle structure is selected for a particular steam flow application, but the entire condensate removal device is adapted to be replaced with other identically configured devices having different size constricted passageways for varying steam flow applications.
These and other continuous flow condensate removal devices are designed to discharge the accumulated condensate while at the same time prevent the passage of live steam. The devices must also discharge the condensate at a rate sufficient to prevent the condensate from backing-up into the steam piping and interfering with the steam system. In order to achieve this balance of operation, the constricted passageway within the nozzle must be provided with an appropriate configuration, including length and diameter, which depends on the characteristics of the mixture of steam and condensate. Different characteristics of the mixture, for example pressure, temperature and percent condensate, require different size constricted passageways.
The diameters of the constricted passageways in continuous flow steam condensate removal devices are sometimes required to be very small, for example, in the range of two one-hundredths to two-tenths of an inch. In addition, this intermediate constricted section must generally be preceded by a converging entrance section. An appropriately configured diverging exit section immediately following the intermediate constricted section is also necessary to eliminate turbulence in the flow of the discharging condensate that could interfere with the flow through the constricted passageway. Since present nozzle structures consist of a single, elongated piece, these size and configuration constraints make manufacturing an appropriate internal constricted passageway difficult. Some optimum sizes and configurations cannot efficiently be achieved within the nozzle structure using current machining and drilling techniques.
Furthermore, although most continuous flow condensate removal systems employ screens and filters to remove particulate debris contained in the mixture of steam and condensate, corrosive products and other debris have been known to pass through to the nozzle structure and collect on the surface of the internal constricted passageway. This reduces the diameter of the constricted passageway, thereby interfering with the operation of the device. Manufacturers of continuous flow devices have attempted to prevent the build-up of corrosion by-products by coating the constricted passageway with a non-stick substance, for example a fluorocarbon material, such as Teflon.RTM.. However, the unitary construction of presently employed nozzle structures makes preparation of the surface of the internal constricted passageway, including de-burring, cleaning and heating, difficult. The added difficulty of applying a uniform thickness of Teflon.RTM. to the inner surface of the constricted passageway makes this process cost-prohibitive.